1. Field of the Invention
The present invention relates to rotorcraft control systems. More specifically, the present invention relates to rotorcraft control systems that are electrically actuated. Even more specifically, the present invention relates to electrically-actuated collective control systems for rotorcraft. The present invention further relates to rotorcraft control systems in which rotor blades are actuated in a manner that obviates the need for a swashplate. The present invention further relates to electro-mechanical torque decoupling mechanisms.
2. Technology Review
Rotorcraft such as helicopters commonly make use of a complex mechanical device known as a “swashplate” to control collective pitch (for providing a change in altitude) and cyclic pitch (for providing change in attitude, and thus maneuvering). By actuating the angles of attack of the rotor blades, each of which is capable of rotating at its root, where it connects to the rotor head, the collective and cyclic pitch of the helicopter can be controlled.
The swashplate, which comprises a non-rotating lower plate movably connected to a rotating upper plate by bearings, is typically located just below the rotor head on the axis of the main rotor shaft, and is itself typically actuated by hydraulic cylinders mounted to the chassis. When rotorcraft controls actuate the hydraulic cylinders, the hydraulic cylinders move and pitch the non-rotating lower plate up and down and at an angle with respect to the plane of the main rotor. This up-and-down movement and/or pitch is transferred to the rotating half of the swashplate. The rotating half of the swashplate thereby transmits the motion of the stationary actuators to the several rotating pitch links, which connect the upper plate of the swashplate to the blade roots and act as lever arms, increasing or decreasing the blades' angle of attack.
A swashplate, however, disadvantageously adds weight and aerodynamic drag to a rotorcraft, which can in turn reduce power, speed, maneuverability, and increase cost of flight. Another major disadvantage of a swashplate is that it limits control inputs to one per revolution of the rotor blades (except in the case of a three-bladed rotor). In addition, because of its mechanical complexity and the fact that it provides a single point of critical failure, swashplates necessitate many hours of inspection and preventative maintenance. The pitch links of a swashplate, which occupy a relatively large volume on the upper side of a rotor shaft and are therefore difficult to shield, also introduce significant ballistic vulnerability, as from missile attack, flak, and other flying debris. Damage to any one of the pitch links results in a loss of rotorcraft control.
What is needed is a system that would eliminate the need for a swashplate to provide robust collective control while still providing root control of rotor blades for cyclic control. What is also needed is a system with a service life similar to a swashplate system without the swashplate's limitations. What is also needed is a system that could realize the considerable performance increases possible if control inputs could be made at a frequency higher than once per revolution. What is also needed is a control system with lower weight and reduced fuel usage, better aerodynamics, reduced ballistic vulnerability, reduced costs, improved reliability and/or the like. Having lower weight and thus reduced fuel usage reduces the carbon footprint of the rotorcraft. It is an object of the present invention to provide a system with one or more of these advantages over traditional swashplate rotorcraft.
U.S. Patent Application Publication 2009/0269199 A1 to Rudley et al. describes a system that provides individual control of rotorcraft blades at the blade root by means of electric motors powered by electric generators that in effect siphon the electrical power needed to rotate the blades off the motion main rotor shaft. Some redundancy is provided both in the generators and the motors. However, the system of Rudley et al. requires multiple rotating-frame motors per blade, giving the system a high weight, and contains no provision for decoupling damaged or inoperable motors from the system during operation, meaning that remaining operable motors must work against the resistance of inoperable motors, an impossibility if the inoperable motors have seized due to damage or wear. Furthermore, in the system of Rudley et al., adverse combinations of generator and motor failure may result in catastrophic total system failure, which may lead to loss of life, even if a majority of generators and motors are operable. Moreover, the system of Rudley et al. requires at least as many functional motors as blades for the continued operation of the system. Additionally, the system of Rudley has inherent backlash throughout the system due to the types of gears and parts needed for the individual blade control system. Further, the system of Rudley requires elaborate effort to maintain or upgrade the system as the numerous blade actuation motors surround the blade roots and connect to them in multiple places, rather than being packaged as easily-replaceable modular units that could be swapped out with a minimal number of system disconnects.
What is needed is a system capable of providing collective control with fewer total electric motors to reduce the amount of weight both of the overall rotorcraft and especially in the rotating frame of the rotor hub. What is also needed is a system capable of providing robust collective control under battle conditions where combat damage may result in reduced operability or failure of critical system components, and where such components may need to be disconnected from the overall system. What is also needed is a collective control system that balances redundancy of critical system components with weight considerations. What is also needed is a system capable of providing power to on-blade actuation systems without requiring heavy and failure-prone power generators in the rotating frame. What is also needed is a system capable of operating with fewer functional motors than blades. What is also needed is a system that reduces or eliminates backlash throughout the system to provide rotorcraft controls of rapid and reliable responsiveness. What is also needed is a system that packages the actuation systems as line replaceable units (LRUs) to reduce system manufacturing and maintenance costs. It is an object of the present invention to provide a system with one or more of these advantages over the system of Rudley et al.
To achieve swashplateless primary flight control in helicopters, on-blade control is required both to provide cyclic control for maneuvering and to ameliorate high levels of vibration and noise. High levels of vibration in rotorcraft cause various problems, including structural fatigue, pilot fatigue, reduced rotorcraft readiness, and increased costs of development and maintenance. Current helicopters typically employ passive vibration isolation and absorption to reduce fuselage vibration. However, these passive devices are heavy and have various other limitations. Past attempts to further reduce vibration have used active techniques such as higher harmonic control of the swashplate and individual blade control by means of active pitch links at the root of each blade.
What is needed, therefore, is a system capable of collective control which can be combined with systems for providing on-blade control. The present invention accommodates on-blade control to provide a comprehensive, cost effective, robust solution to improve rotorcraft performance.